1. Field of the Invention
The present invention relates to a voltage interpolation buffer, and more particularly, to a voltage interpolation buffer by controlling a ratio of bias currents of two differential voltage-to-current conversion units to adjust weightings of input voltages for further outputting an interpolation result of the input voltages.
2. Description of the Prior Art
In the design of driving circuits, especially driving circuits of display devices, a voltage interpolation buffer is a common circuit unit for generating analog interpolation voltages needed by the driving circuits according to inputted reference voltages. However, in the prior art, realization of such functions usually needs an interpolation voltage generation unit for generating the interpolation voltages, as well as a voltage buffer for providing sufficient driving capability.
Please refer to FIG. 1. FIG. 1 is a schematic diagram of a prior art voltage interpolation buffer 10. The voltage interpolation buffer 10 includes a first voltage input terminal VI1, a second voltage input terminal VI2, an interpolation voltage generation circuit 11 and a voltage buffer 15. The first voltage input terminal VI1 and the second voltage input terminal VI2 are utilized for receiving a first voltage V1 and a second voltage V2, respectively. The interpolation voltage generation circuit 11 is coupled to the first voltage input terminal VI1 and the second voltage input terminal VI2, and is utilized for generating an interpolation voltage VS lying in-between the first voltage V1 and the second voltage V2 according to the first voltage V1 received by the first voltage input terminal VI1 and the second voltage V2 received by the second voltage input terminal VI2. The voltage buffer 15 is coupled to the interpolation voltage generation circuit 11, and is utilized for outputting a voltage buffering result through the voltage output terminal Vout. Therefore, the voltage interpolation buffer 10 utilizes the interpolation voltage generation circuit 11 for generating the demanded interpolation voltage VS, and then utilizes the voltage buffer 15 for buffering the voltage outputted by the interpolation voltage generation circuit 11 to be provided with a larger driving capability. As for operations of each part of the voltage interpolation buffer 10, detailed description is illustrated in the following.
Please refer to FIG. 2. FIG. 2 is a schematic diagram of the interpolation voltage generation circuit 11 in FIG. 1. The interpolation voltage generation circuit 11 includes a voltage division circuit 12 and a switch circuit 13. The voltage division circuit 12 comprises resistors R1-Rn, which are coupled in series and coupled between the first voltage input terminal VI1 and the second voltage input terminal VI2, and is utilized for generating division voltages VD0-VDn according to the input voltages of the first voltage input terminal VI1 and the second voltage input terminal VI2. The switch circuit 13 is coupled to the voltage division circuit 12, and is utilized for switching to output one of the division voltages VD0-VDn generated by the voltage division circuit 12 according to a control signal Ctrl.
As shown in FIG. 2, the switch circuit 13 can comprise a plurality of switches SW. Therefore, the interpolation voltage generation circuit 11 can generate the division voltages VD0-VDn through the voltage division circuit 12, for the switch circuit 13 switching to output an interpolation voltage VS lying in-between the first voltage V1 and the second voltage V2. Generally speaking, with regard to the interpolation voltage generation circuit that utilizes series resistors for generating the interpolation voltages, the resistance value of the resistors R1-Rn has to be increased for the purpose of reducing current consumption, so as not to further consume too much power. Mostly, the methods for increasing the resistance value in integrated circuits can be generalized as two kinds: one is to use high resistance materials; and the other is to increase circuit layout area. However, both of the two methods will increase the production cost of the integrated circuits, which is one of the disadvantages of the prior art voltage interpolation buffer 10.
Please refer to FIG. 3. FIG. 3 is a schematic diagram of the voltage buffer 15 in FIG. 1. The voltage buffer 15 includes a transconduction input stage 150 and a load stage 155, and is utilized for outputting the voltage buffering result through the output terminal Vout according to the voltage received by the input terminal Vin. After receiving the voltage signals via a first input terminal 151 and a second input terminal 152, the transconduction input stage 150 outputs corresponding currents Id1 and Id2 to the load stage 155 through a first current output terminal 153 and a second current output terminal 154. The load stage 155 then outputs the corresponding voltage from the output terminal Vout according to the currents Id1 and Id2 of the first current output terminal 153 and the second current output terminal 154. Note that, the first input terminal 151 is coupled to the input terminal Vin, and the second input terminal 152 is coupled to the output terminal Vout. Therefore, by the way of feedback control, the voltage buffer 15 can output a voltage with a value equal to that of the voltage received by the input terminal Vin from the output terminal Vout, so as to achieve the function of voltage buffering.
Please further refer to FIG. 4. FIG. 4 is a schematic diagram of a circuit embodiment of the voltage buffer 15. The transconduction input stage 150 includes a differential pair 156 comprising transistors T1 and T2 and a bias current source CS; and the load stage 155 includes resistors R1 and R2, wherein the transistors T1 and T2 are a pair of matched transistors, the bias current source CS is utilized for providing a bias current of the differential pair 156, and the value of the resistor R1 is equal to that of the resistor R2. Therefore, when the input terminal Vin receives the interpolation voltage VS outputted by the interpolation voltage generation circuit 11, the voltage buffer 15 can convert the received differential voltage signal to the current signal through the transistors T1 and T2, and then output to the resistors R1 and R2. At last, the voltage buffering result is outputted from the output terminal Vout with larger driving capability.
In the prior art, the voltage interpolation buffer 10 has to combine the interpolation voltage generation circuit 11 and the voltage buffer 15 to achieve the function of voltage interpolation and voltage buffering. However, in this way, the resistor string has to be used for generating the division voltages, so as to increase the layout area of the integrated circuits and complicate the fabrication process, with a result that the production cost of the integrated circuits is increased.